Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.94   5.427%   $246.6359   $246.64   $246.65   $246.60  
  Purchase #2 $25.78   11.477%   $28.7388   $28.74   $28.75   $28.70  
  Purchase #3 $30.91   4.742%   $32.3758   $32.38   $32.40   $32.40  
  Purchase #4 $234.91   4.183%   $244.7363   $244.74   $244.75   $244.70  
  Purchase #5 $209.56   9.710%   $229.9083   $229.91   $229.90   $229.90  
  Purchase #6 $5.96   3.396%   $6.1624   $6.16   $6.15   $6.20  
  Purchase #7 $11.87   10.177%   $13.078   $13.08   $13.10   $13.10  
  7 purchase totals = $752.93       $801.6355   $801.65   $801.70   $801.60